WHen I bake I just use a "normal" recipe and use dairy-free margarine (Pure sunflower or Vitalite). If you need to use milk, I use Oatly oat milk.
I made one recently and it was nice - I think having the marg out the fridge for a while helped.
225g (8 oz) unsalted butter, softened or soft margarine
225g (8 oz) caster sugar (although I used a bit less)
4 eggs
225g (8 oz) self-raising flour, sifted
2 tsp baking powder
pinch of salt (I didn't add this!)
Preheat over to 190c/375f/gas mark 5
Grease and line two 20cm (8 inch) sandwich tins
Put butter in bowl, then add the sugar and use a wooden spoon to beat until smooth and light.
Gradually beat in the eggs, ensuring mixture stays snooth,
In a separate bowl sift flour, baking powder and salt, then fold in the egg mixture using a figure of eight movement,
Divide mixture between the sandwich tins and back for about 25 mins until golden brown and risen.
Remove from oven and leave to cool for 5 mins before turnout out on a wire rack to cool completely.
(We put jam in the middle and icing sugar mixed with water for the top). It is really easy and tasty to make (Murray did a lot of it!!!) - I found it a bit too sweet (I have a sweet tooth) so I would maybe reduce the sugar a little. It doesn't take long to make so you could do a test run before the big day?
Hope she has a lovely day xxx